Hi Herve,
Here is a way of preventing users from seeing Ring selection/volume etc if you choose Disabled
Complete these steps:
From the Cisco Communications Administration page, choose Device > Phone, and click the phone.
Choose Disabled for the Settings Access parameter under the Product Specific Configuration section.
When Settings Access is enabled, you can change the phone network configuration, ring type, and volume on the phone. When you disable Settings Access, the Settings button is completely disabled and no options appear when you press the button. Also, you cannot adjust the **ringer volume or save any volume settings. The option Restricted is available in Cisco CallManager version 4.1(3) and later. When you change Settings Access to Restricted, you can only access User Preferences and volume settings. By default, Settings Access is enabled.
From this doc;
http://www.cisco.com/en/US/products/hw/phones/ps379/products_qanda_item09186a00800a6763.shtml
Cheers!
Rob